Error evaluation
The interface pointer ipResultMessage of type I_TcMessage provides information about a current event (runtime message). The most important methods and properties are described below:
Methods
Name | Description |
|---|---|
EqualsToEventEntryEx | Compares the event definition of the event with another event definition. |
RequestEventText | Returns the text for the event. |
Properties
Name | Type | Description |
|---|---|---|
eSeverity | TcEventSeverity | Returns the severity. |
EventClass | GUID | Returns the unique ID of the event class. |
nEventId | UDINT | Returns the ID of the event. |
stEventEntry | TcEventEntry | Returns the event definition. |
For details about the interface I_TCMessage, see the documentation for the Tc3_EventLogger library.
Each event is unambiguously described by the structure TcEventEntry. It contains three structure elements:
- Event-Class
- Event-ID
- Event-Severity
Several events are merged into one event class. For example, the event class for DALI and the event class for EnOcean can contain the event ID 100. The complete description of an event always consists of the event class and the event ID. This avoids ambiguities due to the same IDs within different libraries.
In order to make the events accessible to the PLC, TwinCAT automatically creates a structure for each event class in the type system.
This happens for all PLC libraries that are referenced in the project. The structure ST_DALIEventClass is added using the Tc3_DALI library.
This structure contains all events of the event class for the Tc3_DALI library. Each element of the structure is mapped by a variable of type TcEventEntry. The name of the element indicates the meaning of the event.
TYPE ST_TcDALIEventClass:
STRUCT
NoResponseFromDALITerminal: TcEventEntry := ( …
NoResponseFromDALIDevice: TcEventEntry := ( …
CommandBufferOverflow: TcEventEntry := ( …
[…]
END_STRUCT
END_TYPE
All event classes are stored in the global variable list TC_Events, which is also generated automatically by TwinCAT.
VAR_GLOBAL CONSTANT
[…]
TcRTimeEventClass: ST_TcRTimeEventClass;
Win32EventClass: ST_Win32EventClass;
TcDALIEventClass: ST_TcDALIEventClass;
END_VAR
Thus all messages of all event classes are available in the PLC program.
FAQ
How can I query whether an FB returns an error?
In all libraries, the event ID for error-free execution is set to 0. Since the event ID not only outputs errors, but also notes and warnings, most function blocks have the output bError. This output is TRUE when an error occurs.
IF (fbDALI.bError) THEN
…
END_IF
This output remains FALSE in the event of warnings or notes. Therefore it may be the case that the event ID (fbDALI.ipResultMessage.nEventID) is not 0, but bError remains FALSE.
How can I query whether a FB returns a specific event?
The method
ipResultMessage.EqualsToEventEntryEx(stOther TcEventEntry)
compares whether the event matches the transferred event stOther. Since a variable of type TcEventEntry automatically exists for each event, the query for a certain event can be carried out as follows.
IF (fbDALI.ipResultMessage.EqualsToEventEntryEx(
TC_EVENTS.TcDALIEventClass.NoResponseFromTheDALIDevice)) THEN
…
END_IF
Alternatively, the Event ID can also be queried directly.
IF (fbDALI.ipResultMessage.nEventId = 2) THEN
…
END_IF
A structure of the data type TcEventEntry exists for each event. This is located inside the structure TcDALIEventClass (data type ST_TcDALIEventClass). The meaning of the message is recognizable from the names of the individual events. The use of this structure can thus improve the readability of the PLC program:
IF (fbDALI.ipResultMessage.nEventId =
TC_EVENTS.TcDALIEventClass.NoResponseFromTheDALIDevice.nEventId) then
…
END_IF
For a list of all events that represent an error, see Runtime messages.
How can I query the text of an event?
The text that is output in the TwinCAT Logged Events window can also be queried in the PLC program using the method
ipResultMessage.RequestEventText(nLangId DINT, sResult REFERENCE TO STRING, nResultSize UDINT)
.
If an event is present, the following sample returns the event text:
sTxt : STRING(255);
sEventText : STRING(255);
IF (fbDALI.ipResultMessage.RequestEventText(1031, sTxt, SIZEOF(sTxt))) THEN
UTF8_TO_STRING(ADR(sEventText), ADR(sTxt), SIZEOF(sTxt));
END_IF
The first parameter specifies the language in which the text is to be read. The Tc3_DALI library contains all texts in English (1033) and German (1031).